Forest harvesting operations require West Fraser to build, maintain and repair thousands of kilometres of forest access roads. Here’s one example of how we develop smart solutions to maintain and protect these roads.
ENGINEERED LOGJAM PROJECT
One June, a flood changed the channel of the Gregg River. The new flood-adjusted flow eroded boulder rip-rap that was protecting a road abutment to a bridge owned by Hinton Wood Products. New rip-rap was placed in July to temporarily protect the eroded road abutment from further damage. However, after the water levels receded, the bridge abutment required a more permanent repair.
Traditionally, this issue would be fixed by installing more rip-rap or by diverting the river channel back to its original location. These alternatives have long-term effects on fish habitat and are costly to install and maintain. With fall spawning season for fish like bull trout and mountain whitefish rapidly approaching, Hinton’s woods team needed to install protection for the abutments before the next flood season.
Hinton worked with a consulting firm specializing in water-based construction projects, Alberta Environment and Sustainable Resource Development and Fisheries and Oceans Canada to develop an innovative solution: build a logjam.
The project objectives were to:
- Protect the bridge abutments from erosion and damage by the river’s new course
- Improve the river’s angle of approach to the existing bridge opening to reduce long-term flooding, erosion and ice/debris jam risks
- Minimize habitat disturbance during construction and improve aquatic and riparian habitats
Natural logjams are features on larger waterways that maintain key ecological functions, including the creation of fish habitat. Logjams can also divert water flow or cause unanticipated channel migration that can threaten roads and stream crossings. In this case, the team decided to engineer a logjam that purposefully diverted the river’s flood-changed flow from the road abutment.
Large white spruce and balsam poplar trees growing in the nearby area were tipped over with an excavator and whole trees were moved to the project site. Workers removed dirt from the tree rootwads with hand tools and a high pressure water pump, taking care to keep dirty water from running into the river. Then, over two late October days, the excavator operator carefully placed the cleaned trees in an overlapping pattern in the channel. This pattern weaved a strong logjam that could withstand future floods. To anchor the man-made logjam, anchors were made from tree posts and saddles (large boulders connected by heavy chains) were placed over the logs to make sure there would be no unintended movement of the logjam.
Direct placement of the cleaned trees onto clean gravel and cobble stones eliminated sediment entering the channel from the worksite. The response of the fish to the new logjam habitat was amazingly fast. Within ten minutes of placing one tree, migrating mountain whitefish appeared in the pool under the log's rootwad and stayed there for the rest of the installation.
In a summer 2012 flood, the new logjam held and accumulated more logs as the river moved them downstream. This periodic wood recruitment will naturally replace the original logs over time, maintaining the logjam and continuing to meet the original project objectives.
This project demonstrated innovation to lessen installation impacts, protect road safety and created a “natural” ecological feature that improved fish habitat all at a total cost considerably less than alternative solutions.